Nature of the abnormally high photocurrent relaxation time in the a-Ga2O3-based Schottky diodes

Ga₂O₃ is an ultra-wideband material with excellent optical characteristics. It is a promising material for power applications and optoelectronics because of its high electrical breakdown voltage and radiation hardness. It is optically transparent for visible light and UVA but UVC-sensitive. One of the main disadvantages of this material is the anomalous slow photoeffect: photoconductivity rise and decay characteristic times can be more than hundreds of seconds long. This "slow" photoconductivity effect severely limits the utilisation of the Ga₂O₃-based devices. The aim of this work is the investigation of the nature of this effect. The results of the photoinduced current rise and decay under 530 nm and 259 nm LED are measured in the HVPE-grown α-Ga2O3-based Schottky diode. Upon UV-illumination the photocurrent rise consists of three parallel processes: fast signal growth, slow growth and very slow decay with characteristic times near 70 ms, 40 s and 300 s respectively. Subsequent 530 nm LED illumination resulted in photoinduced current rise consisting of two mechanisms with characterisatic times 130 ms and 40 s on which a very slow decrease of the photocurrent amplitude with characteristic time of 1500 s was superimposed. 530 nm illumination stimulates this process. Protoinduced current relaxation analysis shows the presence of the deep levels with energies (E_C - 0.17 eV). It is suggested that extremely slow relaxations can be associated with potential fluctuations near the Schottky barrier.

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